Pumps are generally useful whenever the transfer of gas or liquid is desired. Manually operated pumps are often more convenient for transferring gases or liquids at remote sites than motorized pumps due to their relatively lighter overall weight and better portability. Manually operated pumps are especially useful for inflating pneumatic tires or inner tubes of bicycles with a gas such as air.
Generally, manually operated bicycle pumps of the prior art provide compressed air by moving a piston longitudinally within a cylinder (i.e. a stroke) to thereby pressurize the air within the cylinder. The pressurized air may then be transferred from the cylinder to a receiving tube or tire via a valve. The volume of air compressed per stroke of the piston is generally a function of the diameters of the piston and the cylinder, as well as the length of the cylinder.
These prior art pumps typically comprise a cylindrical body, a piston, and a piston rod. The piston is typically positioned in the cylindrical body and connected to the piston rod which is also typically positioned within the cylinder. The piston rod is typically directly aligned with a handle or, in some embodiments, comprises the handle itself. The piston rod and piston are moved longitudinally within the cylindrical body by moving the handle in a sliding action stroke relative to the body of the pump.
Manually operated bicycle pumps of the prior art generally fall into two classes, namely, hand-held pumps and floor pumps. Prior art hand-held pumps are operated by holding the body of the pump in one hand and pumping the piston via the piston rod and handle with the other hand in a sliding action stroke. The requisite sliding action stroke forces the user to pump by drawing both hands together (an "inward stroke") and apart (an "outward stroke") along a single axis. The user must essentially use one hand to anchor and stabilize the body of the pump while the other hand either presses the handle toward, or draws the handle away from, the body of the pump. Air is transferred to the receiving tube as the piston generates pressurized air within the cylinder.
Such a sliding action stroke along a single axis using both hands relies for effectiveness primarily on the arm and hand strength of the user. Moreover, the level of force which the user must exert increases as the pressure within the receiving tube increases. To reduce the force the user must exert at any one time as the pressure within the receiving tube increases, some pumps employ a smaller piston diameter. The smaller piston diameter reduces the force required to operate the pump, but correspondingly reduces the volume of air transferred per stroke. Thus, such pumps are less efficient per stroke.
Some manually operated pumps of the prior art attempt to compensate for this reduced volume of air transferred by utilizing a double stroke action. A double stroke action pump enables gas transfer (i.e. gas pressurization within the cylinder) when the piston moves in either direction within the cylinder. Thus, gas within the cylinder is pressurized when the user draws his or her hands together along a single axis (an "inward" stroke) as well as when the user draws his or her hands apart along the same axis (an "outward" stroke).
Such double stroke pumps of the prior art typically comprise two compression chambers: an outer compression chamber from which air is transferred on inward strokes and an inner compression chamber from which air is transferred on outward strokes (or vice versa). The outer compression chamber generally comprises a first cylinder, while the inner compression chamber generally comprises a second cylinder which lies nested within the first cylinder. The inner compression chamber of such pumps generally have a smaller maximum cross-sectional area than the outer compression chamber. Thus, a correspondingly smaller volume of gas can be transferred on the outward stroke relative to the inward stroke. The size of both compression chambers is further limited due to the desirability of minimizing the overall size of hand-held pumps.
A drawback of conventional double stroke action pumps is the complexity of the valve structure required to port air from the nested compression chambers. Such valve structure typically requires numerous mechanical check valves. Moreover, these pumps still require the user to use one hand to stabilize the body of the pump (i.e., the outer cylinder) while the other hand effects the sliding action stroke (i.e., together and apart) motion between the body of the pump and the handle.
Floor pumps of the prior art are designed such that the body of the pump (i.e. the cylinder) rests upon a relatively immobile surface such as the ground or floor. The weight of the pump itself as it rests upon the immobile surface, or the weight of the user's feet resting on the pump, serves to anchor the body of the pump. This obviates the need for the user to use one hand to stabilize or anchor the body of the pump. The user is thereby generally freed to use one or both hands to move the piston rod and attached piston (via the handle) in the cylinder.
In dynamic operation, floor pumps of the prior art draw air into the cylinder (i.e., the "chamber") as the handle is pulled axially away from the pump body (an "upward" stroke). Air in the chamber is compressed and transferred to the receiving tube as the handle is axially depressed toward the pump body (a "downward" stroke).
Prior art floor pumps take advantage of the user's body weight and a set of human musculature stronger than arms and hands to allow the user to exert greater force against the piston on the downward stroke than can be achieved with a hand-held pump. A greater available force to move the piston allows these pumps to be designed with a larger piston diameter which results in the delivery of greater volumes of air at a higher pressure to the receiving tube or tire.
Floor pumps of the prior art commonly use a single u-cup seal in combination with the piston to alternately seal and open the chamber on the downward and upward strokes, respectively. Such u-cup seals generally comprise a convex face and a concave face. Typically, the convex face of the u-cup seal abuts the piston, while the concave face of the u-cup seal faces the chamber. Generally, when held in a static position, an annular gap exists between the perimeter of the u-cup seal and the inner surface of the chamber.
In dynamic operation, as the air in the chamber is compressed on a downward stroke, the pressurized air is forced against the concave face of the u-cup seal causing the outer perimeter of the u-cup seal to flare open and lie flush against the inner surface of the chamber. The u-cup seal thereby substantially effects a seal and restricts the escape of air through the annular gap (i.e., the space between the outer perimeter of the piston and the inner surface of the chamber).
As the user draws the handle upward, a vacuum is created in the chamber. The vacuum draws air into the chamber through the annular gap. The force of the air entering the chamber presses against the convex face of the u-cup seal causing the u-cup seal to collapse thereby allowing the passage of air through the annular gap and into the chamber. Generally, the annular gap is sufficiently large to avoid back pressure problems as the air in the cylinder above the piston is compressed on the upward stroke.
A drawback of the prior floor pumps is that they are generally heavier and bulkier than most hand-held pumps. In contrast, a desirable feature of a bicycle pump is its ease of portability. In addition to being relatively light and compact, a popular, commercially available, manually operated bicycle pump is a hand-held pump designed to attach to the frame of a bicycle for ease of portability when not in use. However, all portable prior art pumps are designed to be detached from the bicycle frame when in use to inflate a tube or tire. This requires the user to detach the pump prior to use, then reattach or re-anchor the pump to the bicycle frame for subsequent transport.
The prior art fails to provide a hand operated bicycle pump which: (1) is portable on the frame of a bicycle and need not be detached from the bicycle frame when in use; (2) transfers substantially the same volume of air to the pneumatic tube or tire on both inward and outward strokes; (3) employs a double u-cup seal structure in the piston head assembly; (4) employs a flex valve structure to seal or open an air inlet port; or (5) anchors the body of the pump such that the user is free to use a more efficient set of human musculature to operate the pump.